The membrane properties, electrical coupling and synaptic interactions of photoreceptors and second order cells, (horizontal cells and bipolar cells) in the vertebrate retina will be studied using electrophysiological, pharmacological, and morphological techniques. The electrical characteristics and organization of electrical coupling between photoreceptors and between horizontal cells will be determined by recording simultaneously from pairs of cells using two electrodes. Electrical interactions will be studied directly by passing current into one cell while recording the resulting voltage change in the other cell. The analysis of experiments on electrical spread in the receptor and horizontal cell networks will make use of direct measurements of light scattering in the retina. The intercellular diffusion of an intracellular marker will be used to obtain information about the organization of coupled networks and the molecular nature of the intercellular connections. Electrical measurements and pharmacological agents will be used to explore the properties of ionic channels in photoreceptor and horizontal cell membranes and to test current hypotheses about the events that give rise to their light response. Electrical studies of bipolar cells will focus on the analysis of synaptic noise and potentials with the aim of understanding the mechanism of receptor transmitter release.